Laser isotope separation and the multiphoton dissociation of formic acid using a pulsed HF laser

Evans, Douglas E.; McAlpine, Robert D.; McClusky, F.K.

doi:10.1016/0301-0104(78)85220-3

Cited by 27 publications

(11 citation statements)

References 28 publications

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“…almost collision-free decom~osition in which collisions deactivate excited molecules, red;cing P, and the second a slower decomposition of the collisionally equilibrated hot gas remaining after the pulse. Probability of decomposition in the first process will decrease as pressure increases and intensity may affect channel ratios, while that for the second, P increases with increasing pressure as has often been observed with longer pulses (15)(16)(17) and will depend only on fluence. This dual mechanism is rather similar to that suggested in a previous study of cyclobutanone at lower pressures (4).…”

Section: The Mechanism Of Multiphoton Decompositionmentioning

confidence: 89%

Multiphoton absorption and decomposition studies of cyclobutanone close to the collisionless regime

Back¹,

Evans²,

Adams³

1984

Can. J. Chem.

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. Can. J. Chem. 62, 1525Chem. 62, (1984. Studies of the multiphoton absorption (MPA) and decomposition (MPD) of cyclobutanone have been extended to short pulses (10 and 40 ns fwhm) and low pressures (0.01 -1.3 kPa) spanning conditions from essentially no gas kinetic collisions during the laser pulse to a collisional regime. MPA results are modelled by a rotational hole-filling model with a system relaxation time of 0.07 (kPa ns)-' and no dependence on laser intensity is observed. By contrast, decomposition appears to be more efficient using a 10 ns pulse than one of 40 ns. Results are reported for both major and minor products and a mechanism for MPD consistent with these results is discussed.

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Section: The Mechanism Of Multiphoton Decompositionmentioning

confidence: 89%

Multiphoton absorption and decomposition studies of cyclobutanone close to the collisionless regime

Back¹,

Evans²,

Adams³

1984

Can. J. Chem.

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“…Formic acid, HCOOH, the simplest carboxylic acid, has received a great deal of attention in the literature. Early theoretical 7–11 and experimental 12–18 studies of formic acid identified two primary unimolecular decomposition pathways, decarboxylation (forming CO 2 and H 2 ) and dehydration (forming CO + H 2 O). Studies in the literature agree that dehydration is the dominant pathway, though the two processes have energy barrier heights differing by only a few kcal/mol.…”

Section: Introductionmentioning

confidence: 99%

Diol isomer revealed as a source of methyl ketene from propionic acid unimolecular decomposition

Rogers

Lockwood

Nguyen

et al. 2021

Int J of Chemical Kinetics

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Carboxylic acids are important combustion intermediates, especially regarding the combustion of oxygenates such as ethyl esters. The purpose of this study is to discern the unimolecular decomposition pathways of one such carboxylic acid, propionic acid, using microreactor flow experiments with line‐tunable photoionization mass spectrometry and infrared spectroscopy, along with high‐level electronic structure calculations (CCSD(T)/cc‐pV∞Z//M06‐2X/cc‐pVTZ level of theory) and master equation theory. Microreactor experiments were performed at 300–1500 K, pressures decreasing from roughly 300 Torr to vacuum pressure, and around 100 μs residence times. Primary products are methyl ketene, ketene, ethylene, and methyl radical. Theory suggests the two lowest energy bond fissions are active at these conditions and responsible for the production of ketene, methyl radical, and some ethylene. Importantly, theory revealed the significance of the isomerization of propionic acid to propene‐1,1‐diol, and the subsequent dehydrogenation reaction of the diol as an alternative explanation for the unimolecular formation of methyl ketene. This is predicted to be the dominant thermal decomposition pathway at lower temperatures (up to ∼850 K). Line‐tunable VUV photons allowed for isomer resolution of the products and showed no evidence of the diol of propionic acid surviving until detection, suggesting propene‐1,1‐diol decomposes either to methyl ketene and water rapidly, fragments upon ionization to a distonic ion inseparable from methyl ketene through our detection methods, or never stabilizes as propionic acid well‐skips directly to methyl ketene. Infrared spectroscopy showed no evidence of the decarboxylation of propionic acid at these conditions. Updated rate constants and branching ratios for propionic acid decomposition are calculated and provided for future modeling studies.

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“…A very large body of experimental and theoretical work on infrared multiphoton dissociation (MPD) has been accomplished since such reactions were first described over 20 years ago. − Of that work, a substantial proportion is concerned with isotope-specific MPD. − Isotopic enrichment in the gas phase of small molecules has been accomplished for sulfur, − oxygen, − hydrogen, − silicon 24 and multiple elements from the same compound. − The most extensive work has been done on carbon isotopes and most often with CO 2 lasers. − Carbon istotopic enrichment has been observed in single-wavelength, single-component reactants, − multiple-wavelength (usually two or more CO 2 laser lines) conditions 28-30 and in two-component, two-step processes. − …”

Section: Introductionmentioning

confidence: 99%

“…While the CO 2 laser frequencies are suitable for many MPD reactions, there are important fundamental vibrational frequencies such as the OH and CH stretch in the 2.5−3.5 μm regions and CO stretch in the 5.5−6.0 μm region which can be excited directly at these wavelengths. These frequency regions have been explored by using frequency-doubled CO 2 lasers, , CO, − HF, ,,, spin−flip Raman, optical parametric oscillators, − and others. Most of these sources have a limited tuning, range and exploration of wide regions of the vibrational spectrum relevant to MPD is not possible.…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4] Of that work, a substantial proportion is concerned with isotopespecific MPD. Isotopic enrichment in the gas phase of small molecules has been accomplished for sulfur, [6][7][8][9] oxygen, [10][11][12][13] hydrogen, [14][15][16][17][18] silicon 24 and multiple elements from the same compound. [19][20][21][22][23] The most extensive work has been done on carbon isotopes and most often with CO 2 lasers.…”

Section: Introductionmentioning

confidence: 99%

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Multiphoton Isotope-Selective Dissociation of Formic Acid Molecules under Action of a Free Electron Laser

et al. 1997

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The infrared multiphoton dissociation (IR MPD) of formic acid molecules (HCOOH → CO + H2O) with free electron laser radiation in the 3 μm region (C−H stretch vibrational absorption band) and in the 6 μm region (CO stretch vibrational absorption band) has been achieved using the same laser. Results indicate that initial excitation of this dimer is more efficient for MPD then initial monomer excitation. Carbon isotope-selective MPD has been performed with an isotopic mixture, H12COOH + H13COOH (50% + 50%), at an irradiating wavelength of 5.56 μm. For this mixture, isotopic selectivity s = k 12/k 13 = 23 has been attained as a ratio of the rate constants of the H12COOH MPD and the H13COOH MPD, respectively. The isotopic selectivity for 13C in the naturally occurring mixture (1.1% of 13C-containing molecules) s = k 13/k 12 = 22 has been attained at an irradiating wavelength of 5.90 μm.

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Laser isotope separation and the multiphoton dissociation of formic acid using a pulsed HF laser

Cited by 27 publications

References 28 publications

Multiphoton absorption and decomposition studies of cyclobutanone close to the collisionless regime

Multiphoton absorption and decomposition studies of cyclobutanone close to the collisionless regime

Diol isomer revealed as a source of methyl ketene from propionic acid unimolecular decomposition

Multiphoton Isotope-Selective Dissociation of Formic Acid Molecules under Action of a Free Electron Laser

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